Radio transmitter



Jan. 9, 1940. J w, HAMMOND r AL 2,186,068

RADIO TRANSMITTER Filed June '7,'1938 5 Sheets-Sheet l JOHN M HA MMO/VD' 505mm. [aw/1205 'NVENTORS ATTORNEYS Jan. 9, 1940'. J. w. HAMMOND El AL RADI O TRANSMITTER Filed June '7, 1938 5 Sheets-Sheet 2 Mm mm m INVENTORS NN DNN MUN OWN JOHN w HAMMOND, EOBEET ,5. EOWAED5 ATTORNEYS 1940- J. w. HAMMOND ET AL 2,186,068

RADIO TRANSMITTER Filed June '7, 1958 5 Sheets-Sheet 3 JOHN w HAMMOND, EOBEKTB. EDWARDS INVENTORS J. w. HAMMOND El AL 6 0 RADIO TRANSMITTER Filed June 7, 1938 5 Sheets-Sheet 4 BE 7 JOHN W HAMMOND, fafiffffl [pk/4x05 NvENToRs h @775 fawn 3 M i v 0 ATTORNEYS 1940- J. w. HAMMOND ET AL 2,185,068

I RADIO TRANSMITTER Filed June 7, 1938 5 SheetsSheet 5 BE 5 JOH/V W HAMMOND EOBEE 7 51 {w /4, 05 INVENTORS ATTORNEYS Patented Jan. 9, 1940 UNITED STATES PATENT OFFICE RADIO TRANSMITTER tion Application June 7, 1938, Serial No. 212,320

Claims.

This invention relates to a radio transmitter or the like, and deals more particularly with a multi-frequency transmitter suitable for operation over a Wide range of frequencies.

5 The improved transmitter of this invention is especially adapted for mobile use, such as in aircraft, boats at sea, etc., but may also be effectively used in other situations.

An object of the invention is to provide a transmitter which will operate efiiciently on each of widely differing frequency bands, and which may be easily and conveniently controlled for shiftting from one frequency band to another.

A further object is to provide improved coil :7 changing mechanism which can be operated from a remote point and which serves to shift coils of different inductance values into a radio circuit for tuning the circuit to frequencies in different bands or channels. Another object is to provide such coil changing mechanism in which the inductance values of the individual coils may be changed through rotation of the coils within the mechanism.

Another object of the invention is to provide improved coupling ineansfor connecting the output of the final or radio frequency stage of the transmitter to the antenna. It is desired that the antenna be readily tunable in each of the high and; low frequency channels, and as afeature of the invention a separate antenna tuning network is provided and is arranged to be automatically connected in the coupling means when low frequency channels are used.

Another object is to provide antenna coupling means which serves not only for tuning the antenna to a particular frequency but serves at the same time for tuning the output circuit of the transmitter to the same frequency. It is further desired that the improved coupling means serve also to eliminate objectionable harmonics and involve a minimum of power loss.

It has been found that in many cases Where space is limited, the larger coils necessary for operation on the lower frequencies cannot be accommodated in the transmitter unit itself. This difficulty is peculiar to. apparatus in aircraft and mobile conveyances. Another factor which has handicapped the use of lower frequency transmitters, particularly in constructions for mobile use, is the fact that the higher voltages attending the use of the larger coils presents insulation requirements which are almost impossible to satisfy. To overcome these difliculties we provide mechanically separate units one of which is the main transmitting unit and the other of which is the antenna tuning unit. These units are, however, associated as to control and are operable concurrently with but a single control device. Since these units may be carried at different locations in the aircraft or other carrier, the space difficulty is overcome; and since the higher voltage of the low frequency tuning coils are removed from the main transmitter unit, the insulation problem is solved. At the same time, convenience of control has not been sacrificed since the adjustment of each unit is accomplished concurrently as one.

For changing the tuning of the main transmitter from one channel to another We provide a shaft which carries a number of rotatable coil assemblies, the different coil assemblies being for the tuning of the different radio frequency stages of the transmitter. Upon rotation of the shaft and coil assemblies, different ones of the individual coils are brought into connection in the radio frequency stages so as to change the frequency on which the transmitter operates. To provide oscillations of widely different frequencies we provide a number of crystals resonant at the desired frequencies. A switch which is mechanically associated with the shaft is operable to connect a crystal of the desired frequency in the oscillator stage of the transmitter.

The arrangement is such that when the parts are turned to a position for operation on the lower frequencies, a choke coil is substituted for the usual tuning coil in the final stage of the transmitter, and also a relay operates to connect into the output circuit the equivalent of a pi network. The tuning of the output circuit of the transmitter and the tuning of the antenna are each accomplished by the adjustment of a single reactance in this pi network. This network serves as a filter to eliminate objectionable harmonics and at the same time is very effective in delivering power to the antenna with a minimum of loss.

Other objects and advantages will be apparent as the specification proceeds.

An embodiment of the invention is illustrated in the accompanying drawings in which- Figure 1 is a broken plan sectional view of the main transmitter unit showing the rotatable shaft and the parts mechanically associated with it; Figure 2, a broken sectional view in elevation, of the main transmitter unit, the section being taken as indicated at line 2-2 of Figure 1; Figure 3, a detail sectional view of one of the individual coils, the section being taken as indicated at line 3-.3 of Figure 1; Figure 4, a detail sectional view of the adjustable contact on one of the individual coils, the section being taken as indicated at line 4-8 of Figure 3; Figure 5, a broken vertical sectional View of the antenna tuning unit; Figure 6, a front elevational View of the power mechanism for driving the rotatable shaft; Figure 7, a circuit diagram showing the electrical connections for remote control of the shaft actuating mechanism; Figure 8, a schematic circuit diagram of the'main transmitter unit; and Figure 9, a schematic circuit diagram of the antenna tuning unit.

.In the description of the illustrated embodiment, attention is first called to the electrical circuit of the main transmitter unit as given in Figure 8. The oscillator tube I0 has its output circuit capacity coupled to the grid of a second tube II here used as a buffer or doubler ampliher, and the output of tube II is capacity coupled to the grid of the final amplifier tube I2 which 0perates as a straight class C amplifier on all frequencies. The audiosection of the transmitter circuit has been omitted from the illustrations since such construction is well known and is not involved in the present invention.

The oscillator tube I0 is a beam power tube having connected between its grid and its cathode the crystal circuit I3. In the crystal circuit is the resistor I4 and one of the crystal elements 2I to 28. Switch 2II determines which of the elements 2| to Z8 is included in the crystal circuit. The plate circuit of tube I0 includes one of coils 3I to 38 which comprise the rotatable coil assembly 30. This coil assembly is described more specifically in connection with the mechanical features of the construction which are taken up later. The plate circuit of the tube II includes one of the coils M to 48 which comprise the rotatable coil assembly 45; and the plate circuit of the tube I2 includes one of the coils 5I to 58 which comprise the rotatable coil assembly 50. As clearly shown in Figure 9, each of coils 5|, 52, and 53, which are for tuning purposes, are provided with adjustable intermediate contacts 5|, 52 and 53 respectively.

Each of these intermediate contacts is adapted to make connection with the conductor I5 which makes connection to the blocking condenser I6. The remaining coils 54 to 58 of the assembly50 are choke coils of fixed inductance values and each have the jumper connections 59 by which the end of the coil nearest the plate of tube I2 is connected to conductor I5. Beyond the blocking condenser I6 the lead II extends to the location of the antenna tuning unit.

Referring more particularly to Figure 9 of the drawings, the lead I! is connected to the rotor elements of the switches l8 and I9 each of which, as here shown, is provided with 8 points. Points I, 2 and 3 of switch I8 are connected through the contacts 6| of the relay 60 to the antenna 90. Condensers such as 62 and 63 may be placed in series with any of these points as may be desired. The purpose of such condensers is to aid in tuning the antenna at the higher frequencies. In many instances these condensers may be omitted altogether. Points 5 to 8 of switch I8 are connected through the coupling condenser I0 to ground, and point 4 of this switch is connected through the coupling condenser II to ground. Though points 5 to 8 are connected through a single condenser, it is understood that different condensers may be used in connection with any of these points.

Points I, 2 and 3 of the switch I9 are idle, and

points 4 to 8 are connected to taps on the seconolary coils 64 to 68 respectively. The end points of coils 64 to 68 are connected to individual points on the master inductor 69, the end point of which is connected through contacts 6I of the relay 60 to the antenna.

On the same shaft with switches I8 and I9 is a third switch I9 having its points I to 3 idle and having its points 4 to 8 connected to one side of a potential 80. The other side of the potential is connected through the winding of relay B0 to the rotor of switch I9.

The antenna may be of the trailing wire type commonly used on aircraft, or may be a fixed structure of any suitable type.

The structure of the main transmitter unit is shown more clearly in Figures 1 to 4. The rotatable shaft is designated by the character I00, and thismay be mounted in any suitableway in a frame. In the illustrations given only fragmentary parts of the frame have been shown, it being understood that any suitable structure for supporting the shaft may be used.

In the present construction, the shaft I00 consists of a hollow tubular piece IOI which at its rear end is attached to the end piece I02 by means of the joining piece I03. The end piece I02 extends through the roller bearing I04 in the rear frame channel I05, and thus provides a suitable mounting for the rear end of the shaft. At the front end of the shaft is the end piece I06 which is secured by the joiner I01. End piece I05 extends forwardly through bearing I08 in the frame panel I08 and thus provides a suitable mounting for the front end of the shaft.

Carried on shaft I00 are the three rotatable coil assemblies 30, 40 and 50, previously referred to in connection with the circuit diagram. The coil assembly 30 comprises a collar piece I30 which may be secured to the shaft as by the screws I3I. Secured about the periphery of piece I30 are the 8 coils 3| to 38. Each of these coils is provided with an end tip 39 to which the front end of the coil winding is connected, and an end tip 39* to which the rear end of the coil winding is connected.

' Mounted to a pair of the frame members III] is a pair of spring contact fingers III. Each of these fingers has its extended ends in register with the end tips on the coils 3I to 38, and is adapted to be spread apart as the coil assembly 30 rotates to bring the coil tips into contact with them. One of the fingers III is electrically connected to the plate of tube I0, and the other is electrically connected to a suitable plate potential, so that when one of coils 3|. to 38 is brought into register with them, this coil is then connected in the plate circuit of tube I0.

A second coil assembly 40 comprises a collar I40 similar to collar I30 upon which is carried the coils 4| to 48. A second set of spring fingers H2 is mounted to a pair of the frame members H0 and is so arranged as tobe engaged by the end tips of the coils 4I to 48. Each of the coils on this assembly is connected into the plate circuit of tube II in the same manner as was described with regard to coils 3| to 38.

A third coil assembly 50 comprises the end mounting plates I50 and I5I each of which is secured to shaft I00 in some suitable way as by the collars I52 and screws I53. To the peripheral portions of plates I50 and I5I are mounted the individual coil units 5I to 58. The coil unit 5I, for example, comprises a. pair of end plates I54 and I55. Securing these plates are two conductor bars I56 and I51, and two hollow mounting bars, I58 and I59. Relatively long pins I60 extend through openings in plate I50, through the hollow of bars I58 and I59, and have their threaded ends engaging the plate I5I, to secure the coils firmly in place. If desired, guide pins I50 may be provided on plates I50 and ISI for supporting and positioning the coil structure during assembly. For convenience in inserting and removing the individual coil units from the coil assembly, the front panel I09 is provided with an opening I6| through which the units may be passed and to allow the pins I00 to be inserted and removed. A hinged door 14 normally covers 15 opening |6| and is provided with a filter 14 through which air may be drawn into the casing for purposes of ventilation.

In the coil unit 5|, the coil winding 99 may consist of a number of spaced turns disposed in a helical groove in the core I62. This core is rotatably mounted by means of the shafts I63 and I63 which are journaled in the end plates I54 and I55. The rear end of the coil winding is electrically connected to the shaft I63 and this shaft has its rearward end protruding beyond the end plate I55 providing a prong which, as shown more clearly in Figure 2, is adapted to engage the resilient contact finger 20| mounted on frame member 200 as the coil assembly is rotated to 80 bring it into register with this finger.

Connecting the conductor bar I56 with the coil winding is the rider contact I10 which comprises a resilient piece having its one end provided with a shoe In of insulating material and having its '85 other end provided with a contact nose I12. The nose I12 is grooved at its center and beveled at its edges as shown more clearly in Figure 4. of the drawings. The central portion of the contact piece has the upturned ears I13 which have curved upper edges for slidably engaging the underside of the bar I56, Connecting the conductor bar I51 with an intermediate turn of the coil winding is a second rider contact I15 similar to the contact I10 already described.

The conductor bars I56 and I51 each extend rearwardly beyond end plate I55 to form prongs positioned to engage the resilient contact fingers 202 and 203 mounted to the frame member 200, when the coil assembly is rotated to bring these bars into register with the respective contact fingers.

The extreme forward end of coil shaft 53 is provided with a slot so that the coil may be easily turned by a screw driver extended through the frame opening IGI. It will readily be seen that when the coil shaft is rotated in one or another direction, each of the contact riders I10 and I15 will be moved longitudinally of the coil due to the engagement of the nose I12 with a 60 turn of the winding, to either increase or decrease the inductance included between the contact riders and the coil shaft.

The spring finger contacts 20!, 202, and 203 are each supported by one of L-pieces 204, and 65 are each secured together with the L-piece to the frame member 200. The L-pieces serve to position the spring members when these members are not in register with the contact bars or coil shaft. The finger contact 20! is electrically connected 70 through a suitable plate potential source to the cathode of the tube I2; the contact 202 is connected to the plate of tube I2; and the contact 203 is connected to the conductor I5, previously referred to. With this arrangement, it is clear that the inductance between rider I10 and the center shaft is connected in the plate circuit of the final stage of the transmitter when coil 5| is connected, and that the antenna connection is made to this coil at a point determined by the position of the rider I15.

The above description of the coil unit 5| applies equally as well to each of the coil units 52 and 53, for these units may be identical with coil unit 5| except for the difference in the inductance of the coil winding. The coil units 54 to 58 differ in that they have windings of higher inductance value and serve only as choke coils in the final amplifier stage of the radio circuit. In each of the coil units 54 to 58 one end of the winding is connected to the coil shaft and the other end is connected to one of the conductor bars I58 and I59. Jumper connections 59, already mentioned, connect the bars I56 and I51 together on each of units 54 to 58.

The foregoing describes the rotatable shaft and the coil assemblies which are carried by the shaft. The switching mechanism by which selected ones of the crystal elements are connected into the oscillator stage of the transmitter will now be described.

A crystal plate 2|0, shown more clearly in Figure 2 of the drawings, may be mounted in any suitable way to the frame or chassis of the transmitter. A number of crystals in appropriate crystal holders may be mounted on this plate and may have their leads connected to appropriate points on the rotary switch 2| I. The rotor of switch 2|| has attached thereto the toothed gear 2|2 which makes engagement with the gear 2 I3 secured to the rear end of the shaft I02. The mechanical connection between the rotor of switch 2 and the shaft I00 is such that at the time the shaft is in position to bring coils 5|, 4| and 3| into engagement with their respective contacts, the switch 2|| will be in angular position to bring the crystal 2| into connection with the oscillator circuit of the transmitter. With each of the above named coils connected in the respective radio stages, it is clear that each of these stages will be tuned to the proper frequency. Similarly, when the rotating assemblies are at different angular positions, all circuits will likewise be tuned to the proper frequency.

The drive mechanism 260 by which the coil assemblies are rotated is shown more clearly in Figures 1, 2 and 6. The frame structure 2I5, which carries this mechanism, is secured to the front frame panel I09. Mounted on structure H5 is the electric motor 2|6. The shaft of the motor is provided with a pinion 2|1 which engages the gear 2|8 on shaft 2I9, and a pinion 220 on shaft 2| 9 engages the gear 22| on the drive shaft 222. Shaft 222 is provided with the worm 223 which engages the gear 224 secured on the end shaft piece I06. Thus the motor is connected in direct drive relation with the rotatable shaft and coil assemblies.

The drive shaft 222 extends laterally to the exterior of the frame structure 2|5 and is provided with the hand crank 225 which permits manual actuation of the rotatable shaft I00 when this is desired.

The shaft end I06 extends through a disk 226 which is supported in stationary position by the frame member 221. On this disk are carried spring contacts 228 which extend forwardly and engage the disk 230 which is secured to the shaft end. The extreme forward end of the shaft end I06 has secured thereto a disk 23| which, as shown more clearly in Figure 6, has the numerals to 8 3 having its rotor shaft 3| la extending foron its peripheral portion. The casing or cover jects into the motor drive casing 3| 3 mounted- 232 which encloses the power mechanism is provided with a small window 233 through which one of these numerals is visible from the front of the transmitter unit. The numeral visible through window 233 indicates which of the coils are connected in the circuit and therefore which of the several channels the transmitter is operating on.

The electrical circuit associated with the actuating mechanism is shown more clearly in Figure 7. As here shown the disk 23!! is electrically divided into two segments 234 and 235 which are spaced by the insulating path 236. The contacts 228 (Figure 2) include a pair of contacts 231 and 231a (Figure 7) which made sliding contact with the segments 234 and 235, and also the contacts 8| to 88 which are angularly spaced about the disk 230 and make sliding contact with segments 234 and 235. As clearly shown in Figure 7, the insulating path 236 is angular in form so as to avoid registry with more than one of the spaced contacts 8| to 38L Motor 2|6 preferably has two fields 23B and 239, one of which is adapted to cause the motor to rotate in one direction and the other of which is adapted to cause motor rotation in the opposite direction. One side of the motor is connected to a suitable source of electrical energy 2%, while the other side of the motor has the terminal of field 238 connected to the sliding contact 231a and the terminal of field 239 connected to the sliding contact 231. Energy source 240 is connected by conductor 2 to the rotor element of the switch 250 which may be located at a remote point. Also the contacts 8| to 88 are connected by suitable conductors to points to 8 respectively on the switch 250. These conductors may be enclosed in a single cable, if so desired.

The antenna tuning unit, already described in connection with Figure 9 of the drawings, may be mechanically arranged as illustrated in Figure 5. The structure shown includes a casing 300 to which the mounting structure 3M is secured by the posts 302. Structure 3M comprises the mounting plates 393, 304 and 305 which are spaced and supported by the posts 305. The rotatable shaft 301 is journaled in plates 3%, 3M, and 305 and forms the rotor member of switches |8, I9, and 19. The spring contact arm 308, which is a part of switch I8, is secured to shaft 381 and is adapted to engage one of the contact points I to 8 of this switch; the contact arm 309, also secured to the shaft 301, is adapted to engage one of the contacts to 8 of the switch l9; and a rotor element 1911, also secure with shaft 301, is adapted to engage the stator contacts on switch 19. Switch l8 has its stator points connected to the coupling condensers l8 'and H; switch H) has its stator points connected to the coils 64 to 68; and switch N has stator points connected to the winding of relay 60. Each of coils 64 to 68 are mounted to the plate 383 by a post 3| ll, and each are provided with a tap switch wardly to the front of casing 300 and being adapted for adjustment by the use of a screwdriver. The turning of the shafts 3| la serves to change the electrical connection from one to another of the taps on the respective coils and so effects change in the inductance to be applied to the circuit. The relatively large master coil 89 is mounted in the rearward part of the casing on the posts 3|2 and is provided with intermediate taps.

The front end of the rotatable shaft 30'! proon the casing front. The motor drive mechanism'ZlO contained in casing 3|3 and the electrical connections thereto may be identical with the actuating mechanism 260 shown in Figure 6 and described in connection with the main transmitter unit. As shown more clearly in Figure '7, the electrical conductors leading from mechanism 2m are connected to respective points on the switch 2' which has its rotor element mechanically connected with the switch 256. It will now be clear that as the switches 250 and Ell are operated in unison by a single movement, each of mechanisms 260 and 270 will be caused to operate simultaneously and to the same extent.

Construction such as described herein makes the transmitting apparatus peculiarly adaptable for operation on widely different frequency ranges. For example, the coils 3|, 4|, and 5| may be of such inductance values as to cause their respective circuits to be resonant at a very high frequency such as for transmitter operation at 20 megacycles; the coils 33, 43, and 53 may be of such value as to tune the circuits to lower frequencies in the general high frequency range, for operation on such as 2 megacycles; and coils 32, 42, and 52 may be adapted for operation at such intermediate frequencies as 10 megacycles. The coils 34 to 38, and 44 to 43 may be of such value as to suitably tune the respective circuits to various frequencies in the general low frequency range. For example, these coils maybe suitable for transmitter operation at frequencies ranging between 200 and 800 kilocycles. It is understood, however, that the specific frequencies above given are illustrative only and the apparatus may be arranged for tuning to any desired frequency.

In the illustrations given, the apparatus is shown with the coil assemblies in such position as to connect coils 3|, M, and 5| in the respective circuits of the transmitter unit; in the antenna tuning unit switches I9 and '59 are on idle positions; and the switch i8 is in position i so as to make connection through contacts 6| of relay 60 to the antenna 99, the relay 68 being in released position as as to maintain contacts 6| closed. Also, the switch 2 will be in position so as to connect the oscillating element 2| in the oscillator circuit.

With the apparatus in this position, and. upon suitable potentials being supplied in the appropriate points to produce normal operation of the apparatus, the oscillating element 2| will effect oscillations of, for example, 10 megacycles frequency. Oscillations of this frequency in the plate circuit of tube Iii are fed through the capacity coupling to the grid of tube l. The amplified variations in the plate circuit of tube now doubled in frequency, are fed by capacity coupling to the grid of tube 2. The output of the modulating apparatus (not shown) is also fed into'tube l2, and the output of this tube is fed through conductors I5 and ii to the antenna tuning unit. The blocking condenser H7 prevents transmission of direct current along this path.

Referring now more particularly to Figure 9 of the drawings, it will be observed that the path from conductor l1 through switch I9 is open since the rotor of switch i9 is on an idle point, and that an electrical path is completed through point I of switch l8 condenser 62, and contacts 6| of relay 66 to the antenna 90. Tuning to the carrier frequency may be had'by changing the inductance value presented by coil. 5| in the final stage of the transmitter unit. To effect such adjustment the operator has but to open the door M and with a screwdriver or some similar tool, turn the coil shaft end H53 in one or another direction depending on whether it is desired to raise or lower the inductance value presented by coil 5!. In the construction shown, if the shaft W3 is turned in a clockwise direction, both of riders ill) and H5 will be caused to move forwardly of the coil thereby increasing the inductance value presented by this coil, and also changing the position along the coil at which the antenna connection is made. Thus, rotation of coil 5i serves not only to change the frequency at which the final amplifier stage is resonant, but also to effect the tuning of the antenna to correspond with the new frequency.

Should the operator wish to tune the transmitter to a lower frequency such as, for example, 10 megacycles, and for which the crystal element 2! would not be suitable, he may turn the switch 256 from point i on which it is shown in the illustration, to point 2. As shown more clearly in Figure '7, this completes a circuit from potential source 240, through the motor 2E6 including field 239', to sliding contact 23'! engaging the disk segment 234, from segment 234, through. contact 82 to point 2 of switch 258, and from the rotor of this switch to the other side of source 240. This produces actuation of motor 2M3 in a direction such as to cause rotation of disk 236 in a counterclockwise direction as seen in Figure '7.

Rotation of the shaft of motor 2H5 operates through pinion 2H and gear'2l8 to produce ro tation of shaft M9, and through engagement of pinion .220 with gear 22!, produces rotation of shaft 223; and rotation of worm 223 on gear 222 produces, through engagement with gear 224, the rotation of shaft Hill and the coil assemblies 39, ill, and 50. This movement continues until the insulated path 1'36 of the disk 23! comes into register with the contact 82, when the motor energizing circuit is broken, and rotation of motor M8 ceases. At this position the coil assemblies 353, All and 56 will have moved into such angular position as to bring the coils 32, 42, and 52 into connected position in the transmitter circuits. Referring now more particularly to Figure 2 of the drawings, it will be apparent that the above described rotation of shaft Hill operates through gears M2 and 21; to rotate the switch 2!! so as to connect the crystal element 22 into the oscillator circuit. Thus the mechanism of the transmitter unit has been actuated automatically from a remote point to change simultaneously the crystal element and the tuning coils associated with the various stages of the unit.

Since the armatures of switches 250 and 21! are mechanically connected, the control movement above described also operates to move the position of switch 21! to point 2. As will be observed from Figure 7, this completes a circuit from source 34!! (which may. if desired. be the same as 2M3), through motor 356 including field 339. to the sliding contact making engagement with disk segment 334, and from contact 92 through switch 211 to the other side of source Actuation of motor 3H5 by the above circuit operates to rotate the shafttli'l in the tuning unit, and such rotation changes the positions of switches it, !9, and 15. Since the disks 33D and 233 of mechanisms 210 and 260 respectively are similar, both shafts I00 and 301 will be rctated through an equal angular distance and in the same direction.

When the insulating path 336 of the disk 33!) comes into register with the contact 82, the motor energizing circuit is broken and motor 3l6 stops rotation simultaneously with motor M6. The new position of switches l8, l9, and 19 in the above described operation will be at points 2.

In the new position of the apparatus, and upon suitable application of potential at appropriate points, oscillations of, for example, 5 megacycles will be generated at crystal element 22, and a carrier frequency of substantially 1O megacycles will be delivered through switch It! and contacts 6! of relay 5!! to the antenna.

Similarly the operator at the remote point may move his control switch 250 to point 3 which would cause the coil assemblies in the. transmit ter unit and the switches of the antenna tuning unit to be turned to position for operation on a still different channel in the high frequency range. At each of the angular positions of the coil assemblies adjustment of the inductance value presented by the connected coil in the final amplifier stage may be accomplished by rotation of the connected coil by access through the opening 5!.

If the operator wishes to tune the apparatus to some frequency in the general low frequency range such as 200 kilocycles, he may turn the switch 250 at the remote location to point 8. This completes the circuit through motor field 233 and disk segment 235 which produces rotation of motor H6 in a direction reverse from that above stated, and which operates to rotate the coil assemblies so as to bring coils 38, 48, and 58 into connection in the respective circuits of the transmitter unit. Actuation of motor 3H5 through field 33!! produces rotation of shaft 391 so as to bring switches l3, l9, and it to point 8. Also rotation of shaft I00 operates through gears 2 l3 and 2 i2 to rotate the switch 21 i so as to con nect the crystal element 28 into the oscillator circuit.

In such position of the mechanism the oscillator and first amplifier stages of the transmitting unit will be tuned to the new frequency of 209 kilocycles. The final amplifier stage of the apparatus will also be tuned to the new low frequency, but in a different manner. The coil 58, which is at this position connected to the plate of tube I2, serves as a choke coil only and is altogether ineffective to tune the plate circuit of this tube to the new low frequency. Itspurpose here is only to permit the application of operating plate potential to tube I2.

Referring now more particularly to Figure 9, it will be seen that when switch 19 is on point 8, a circuit will be completed for applying potential from source through the winding of relay 60 for actuating this relay. With switches Ill and IS on positions 8, there will be formed a pi network for coupling the final stage of the main transmitter unit to the antenna. One leg of this pi network will be through point 8 of switch I8 and through coupling condenser iii to ground. The top or bridge of the pinetwork is through point 8 of switch I9, the secondary inductance 68, the master inductance E9, and the now connected contacts 5| of relay 6!! to antenna 99. The second leg of the pi network is formed by the capacitance between antenna and ground.

The equivalent pi network. above described is seen to be in series connection in the plate circuit of the tube in the final amplifier stage of the transmitter, and'adjustment of this net work by variation of the secondary. inductance 68 serves to tune both the output circuit of the transmitter and the antenna. For convenience in accomplishing adjustment of the coil 68 a switch 3| I is provided, and to adjust this inductance the operator may turn shaft 3W from the front of the tuning unit panel with a screwdriver or similar tool. It is an important feature of this invention that by this single adjustment tuning of the amplifier plate circuit and of the antenna is accomplished. The same circuit adjustment may be made effective'on all channels by changing the adjustment of master coil 69.

In the construction shown, each of points 5, t, 7, and 8 of switch I8 are shown connected through a single condenser 10. However, where the different frequencies to which the transmitter is desired to be tuned require coupling condensers in the pi network of different values for convenient operation, individual condensers may be connected to each of these points.

The use of the equivalent pi network in the manner above described provides a very effective way of eliminating objectionable harmonics. The pi network operates in the nature of a filter to prevent such harmonics from being transmitted to the antenna.

While in the illustrated embodiment each of coil assemblies 30 and 40 have individual coils of fixed inductance, it is contemplated that where necessary for tuning to the desired frequencies individual coils on these assemblies may be of the adjustable type as well as the individual coilson the assembly 50.

The remote control of each of the units here provided'presents an advantage in that the direction of rotation of shafts I60 and 301 is such that these shafts will be driven the shortest possible angular distance to reach the desired position. Simultaneous actuation at each of the units with but a single control movement on the part of the operator is deemed an important advantage.

While we have described in detail but a single embodiment of the invention it is understood that many other constructions may be made embodying all or only part of the features herein set forth. Many changes may be made in the arrangement of parts and details of construction without departing from the spirit of the invention.

For example, the specific structure herein described for mounting the rotatable coil assemblies within theframe may be changed to any other suitable structure; and though the described embodiment includes 8 channels. 3 in the general high frequency range and 5 in the general low frequency range, other numbers of channels may be used of any desired frequencies.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood and formed, but the appended claims should be construed as broadly as permissible, in view of the prior art.

What we claim is:

1. In radio transmitting apparatus including an oscillator stage, a radio frequency amplifying stage and an antenna, an oscillator element adapted for high frequency oscillations and an oscillator element adapted for low frequency oscillations, means for selectively connecting said elements in said oscillator stage, a pair of coils adapted to be individually connected in said amplifying stage, one of said coils being of such inductance as when connected in said stage to tune said stage to the frequency ofsaid first-mentioned oscillator element, the other of said coils being of relatively high inductance and ineffective to tune said amplifier stage to the frequency of said second-mentioned oscillator element, means mechanically coupled to said first-mentioned means for connecting said one coil in said amplifier stage when said first-mentioned element is connected in said oscillator stage and for connecting said other coil in said amplifier stage when said second-mentioned element is connected in said oscillator stage, an antenna tuning device, and coupling means for connecting said antenna through said tuning device to said radio-frequency stage when said other coil is connected in the circuit and for connecting said antenna independently of said tuning device to said radio-frequency stage when said one coil is connected in the circuit.

' 2. Apparatus as set forth in claim 1 in which said last-mentioned means comprises a relay controlling the insertion of said tuning device in said coupling means and a switch mechanically associated with said connecting means controlling the operation of said relay.

3. In radio transmitting apparatus including a final amplifier stage and an antenna, a coil tuning said stage to a predetermined frequency, a radio frequency choke coil, switching means for selectively including either of said coils in said stage, a tunable antenna coupling circuit connected with said stage, and a second switch means tuning said circuit when said choke coil is included in said final amplifier stage and directly connecting said antenna and amplifier stage when said first coil is included in said stage.

4. In radio transmitting apparatus including a final amplifier stage and an antenna, a coil tuning said stage to a predetermined frequency, a radio frequency choke coil, switching means for selectively including either of said coils in said stage, an antenna coupling circuit connected with said stage and including a tuning means, and a second switch means operable concurrently with the first for tuning said coupling circuit when said choke coil is included in said amplifier stage and for by-passing said tuning means when said first coil is included in said stage.

5. In radio transmitting apparatus including a final amplifier stage and an antenna, a coil changing device including at least one coil which when connected in said amplifier stage will tune said stage to a predetermined frequency, said device including also at least one radio frequency choke coil which when connected in said amplifier stage serves to deliver potential but is ineffective to tune said stage, coupling means for delivering power from said amplifier stage to said antenna, a tuning network, and mechanically dissociated electrical switching means concurrently operable with said coil changing device for connecting said tuning network in said coupling means when said last-mentioned coil is connected in said amplifier stage by said coil changing device.

JOHN W. HAMMOND. ROBERT B. EDWARDS. 

